Heidi Strbak has pleaded guilty to the manslaughter of her son Tyrell Cobb. File pictureSource:AAP

THE mother of Tyrell Cobb has pleaded guilty to manslaughter this afternoon and it has been revealed she allegedly delivered the blow that killed the four-year-old.

Heidi Strbak appeared in the Supreme Court in Brisbane this afternoon supported by family and friends just weeks after the case made headlines when her ex-boyfriend received a paltry four-year sentence on the same charge.

Tyrell Cobb died in hospital after he was found unconscious at a Gold Coast home. File pictureSource:Supplied

Tyrell was found unconscious inside a Gold Coast home on May 24, 2009, and taken to hospital, where he was pronounced dead.

Police allege he died from a blunt-force trauma injury to his abdomen and had sustained about 70 injures over a period of time.

Strbak and her then-partner Matthew Scown were initially charged with murder, but the charges were downgraded at a committal hearing last year.